Process for preparing the strontium isomorph of colemanite



Aug. 22, 1967 H, WEBER ETAL 3,337,293

PROCESS FOR PREPARING THE STRONTIUM ISOMORPH OF COLEMANITE Original Filed March 28, 19 63 llll'lllllll SYNTHETlC STRONTIUM ISOMORPH a c (/7 3 W M u U M W 29(DIFFRACTION ANGLE) FIG.

MINERAL COLEMANITE 3 FIG.2 Sr ISOMORPH OF COLEMAN'ITE i v I 0.! 6

l/cmm N U1 "(ARBITRARY UNITS) PYROELECTRIC SIGNAL 0130 0 -so -50 -40 -z-o -20 -m o lo 20 3o 40 50 T (DEGREES C) HARRY H. WIEDER F163 ARTHUR R. CLAWSON CHARLES FLPARKERSON ATTORNEY.

United States Patent 01 3,337,293 Patented Aug. 22, 1967 3,337,293 PROCESS FOR PREPARING THE STRONTIUM ISOMORPH F COLEMANITE Harry H. Wieder, Arthur R. Clawson, and Charles R. Parkerson, Riverside, Calif., assignors to the United States of America as represented by the Secretary of the Navy Original application Mar. 28, 1963, Ser. No. 268,845. Divided and this application Oct. 6, 1966, Ser. No.

3 Claims. or. 23-59 The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This is a division of US. patent application Ser. No. 268,845, filed Mar. 28, 1963, for Synthetic Ferroelectric Colemanite and Its Strontium Isomorph.

The present invention relates to synthetic ferroelectric colemanite and more particularly to the strontium isomorph of colemanite.

Colemanite is a mineral calcium borate pentahydrate found in relative abundance in conjunction with other borate minerals. At temperatures generally below 2 C. to 7 C. crystalline colemanite becomes ferroelectrio and remains ferroelectric at least to 180 C. Colemanite is a mechanically, electrically, and chemically stable ferroelectric material. It shows none of the polarization fatigue effects associated with barium titanate nor is it subject to deliquescence at temperatures below +50 'C. as some other water soluble ferroelectric materials. Mineral colemanite contains many impurities. It is difiicult, therefore, to determine the dependence of the desirable electric properties upon the impurity content of a crystal. For switching applications, it is desirable to keep the transition temperature, i.e., the Curie temperature, above +25 C. in order that no refrigeration be required for a computer memory device employing colemanite crystals. For its use as a dielectric bolometer or pyroelectric detector, it is desirable to control the Curie point by additive impurities so that the maximum change in polarization with temperature should occur at some predetermined temperature. Therefore, miner-a1 these aforementioned applications and that the synthesis of the pure compound is required.

It is an object of the invention to provide the synthesis of the strontium isomorph (2SrO-3B O -5H O) of colemanite which represents 100% replacement of calcium by strontium.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 shows an X-ray diffraction powder pattern of strontium isomorph of colemanite.

FIG. 2 shows the X-ray diffraction powder pattern of natural colemanite.

FIG. 3 shows characteristic curves for the strontium isomorph of colemanite.

The publication, Ferroelectric and Pyroelectric Properties of Mineral and Synthetic Colemanite, by H. H. Wieder, A. R. Clawson, and C. R. Parkerson, Journal of Applied Physics, 33, 1720 (1962), describes in detail the results obtained on synthetic colemanite and compares the dielectric and pyroelectric properties of the synthetic compound with the impure mineral.

Colemanite may be synthesized by a two-step reaction. The first step consists of the synthesis of inyoite (ZCaO- 3B O -13H O) synthetic (2CaO-3B O -9H O), or meyerhofierite 2CaO 3B 0 7H O) For these reactions see Reactions 1, 2, and 3 of the Table of Reactions which follows. These higher hydrates may be converted to colemanite (2CaO-3B O -5H by reaction with borax solution. For an example of this conversion reaction see Reaction No. 4. Colemanite can also be synthesized by the preparation of gowerite (CaO- 3B O SH O) or nobleite (CaO-3B O -4H O) as given in Reactions 5 and 7. Reaction of either of these two compounds with borax solution as given in Reactions 6 and 8 will procolemanite because of its inhomogeneity, is not suitedfor duce colemanite.

TABLE OF REACTIONS Reactant I Reactant II Reaction Water N0. Amount Chemical Formula Weight Chemical Formula Weight (grams) (grams) (grams) N212B4O7-10Hz0 1. 67 C2I(IO3)2 Na2B40 -10H2O 1. 67 (NHmBwOw 8Hz0. 1.00 0. 43 NagBrOrlOHzO 1. 71 1. 00 100 3 O3 40. 0 20. 0 100 NazBrOrlOHzO- 2. 24 1. 25 150 5. 29 1.85 100 Nazl34O1-10H2O 2. 24 1. 25 (NH4)2B1@O10-8HiO 16.0 7. 10 800 NazB407-1OH20 2. 24 1. 25 150 NazB4O -1OH20 7. 60 4. 20 200 N8.zB407-1OHzO 4. 50 SrO-B2O3-4Hz0 (Compound VI) 1. 50 150 31303 3. 00 SIO-BzO3-4IIz0 (Compound VI) 1. 50 150 NazB4O -10H2O 2. 24 SrO-3B2O;;-4H2O (Compound IV) 1. 25 150 Na B4O1-10H2O 4. 02 sI(IOa)2-H2O 2. 55 150 Na2BiO1-10I-I2O 2. 24 SrO 3B 03411 0 (Compound V) 1. 25 150 Na2B4O 7'1OH2O 4. 02 SHIO s)z-Hz0 2. 55 150 N3gB407'10H2O 11. 44 SIClz-GH2O 8. 00 200 TABLE OF REACTIONS-Continued Reactant III or Seed Material (if required) Reaction Time Tempcia No. (days) ture, 0. Product Chemical Formula Weight (grams) 34 3O Inyoite (2C2tO'3BzO3 13HzO).

65 Meyerhotferitc (2CaO-3B2O3-7H2O). 41 30 Synthetic (2CaO-3BzO -9HzO). 35 65 Colemauite (2CaO-3B2O3-5I-Iz0).

1 35 Gowerite (CaO-3BzOn-5I-Iz0). 2C2LO-3BzO3-5H2O 65 Colcmanitc (208.0-3BzO3-5Hz0). 8 85 Nobleito (CaO-3B2O3-4H2O). 2CaO-3B2O3-5H2O (-200 Mesh) 19 65 Colemanite (2CaO-3BgO -5I-Iz0).

7 Compound III (S11O-3B2O3-4H2O). 13 65 Compound I (2SrO-3B2Ow5H2O). 7 25 Compound VI (SrO-BZO -4H O). 27 65 Compound I (ZSrO-3BzO -5H O). 13 65 Compound IV (SrO-3B2O 4HQO). 8 65 Compound I (2SrO-3B2O -5HgO). 5 65 Compound V (SrO-B O3-4HzO). 27 65 Compound I (2SrO-3B2O -5H2O). 14 65 Compound I (2S1'O-3B2O3-5H2O). 36 80 Compound I (2S1'O-3B203-5I'I20).

It was suspected at an earlier date (H. H. Wieder, J. Appl. Phys. 30, 1010 (1969)), that the onset of ferroelectricity in colemanite may be strongly influenced by the presence of strontium replacing calcium substitutionally in the crystal-lattice of colemanite.

Partial substitutes of strontium for calcium in colemanite is achieved by preparing the higher hydrate in the presence of the desired strontium ion impurity in the form of a highly ionized strontium compound such as SrCl Sr(NO etc. or a partially ionized compound such as Sr(IO -H O. The higher hydrate is then converted to colemanite with borax solution as previously described. If a higher percentage of replacement is desired, strontium ion may be added to this conversion reaction also.

The discrepancies between various authors as to the exact Curie temperature of colemanite ranging between 0 C. and 7 C. were suspected as due primarily to the variable strontium content of colemanite, i.e., that mineral colemanite is thus a solid solution of calciumstrontium borate pentahydrate. It was proposed, therefore, to produce a synthetic colemanite containing a large amount of strontium instead of calcium. The method is outlined below:

The first step consisted of the preparation of a specimen as follows (for example):

Reactants H O ml 800 Ammonium penta-borate gm 16.0 S1(NO -H O gm 7.10 The ammonium pentaborate was dissolved in 700 Grams Borax 2.24 Specimen preparation described above 1.25 H O 150 The above was heated and sealed at 70 C. and maintained at that temperature for 13 days with continuous agitation by means of a shaker table. A second sample was prepared in an identical manner except that the reaction was allowed to proceed for days. The resultant crystallites are microscopic in size. The Debye-Sherer X-ray pattern, the dielectric properties and the pyroelectric properties were measured. The X-ray diffraction powder pattern of the strontium isomorph of colemanite is shown in FIG. 1. It may be compared with the powder pattern of natural colemanite shown in FIG. 2.

The X-ray powder diffraction pattern of the Sr isomorph bears a striking similarity to that of natural colemanite. The significant similarities are in the lines at the smaller angles. Since these are due to low order hkl reflection there are fewer combinations of h, k, I that can account for them. The similarity in the grouping of these lines indicates a very similar crystal lattice, especially since these lines occur at only slightly different angles. The change in position of the lines is due to slight changes in the interatomic distances in the lattice when Sr is substituted for Ca. The occurrence or extinction of one or two minor lines and the change in magnitude of the main reflections is also due to slight changes in position of the atoms in the lattice.

In order to test the dielectric and pyroelectric properties pressed powder pellets were prepared in accordance with the description in the publication by Wieder, Clawson, and Parkerson aforementioned. FIGURE 3 (l/C curve) shows that the strontium isomorph of colemanite obeys a Curie-Weiss relation since the capacitance which may be considered as proportional to the electrical susceptibility has the typical dependence of ierroelectrics in the vicinity of their Curie temperatures. The Curie temperature of the strontium isomorph shown in FIG. 3 is +30 C. Subsequent measurements performed on other samples established the Curie temperature to be between +30 and +35 C. This is also supported by the pyroelectric data shown in FIG. 3 (1r curve) which illustrates the magnitude of the pyroelectric signal as a function of temperature obtained directly on an XY recorder. The experimental method for obtaining the pyroelectric response is also described in the publication by Wieder, Clawson, and Parkerson.

The data presented here for the colemanite strontium isomorph represent a shift of the Curie temperature from -35 C. for the pure synthetic colemanite to +35 C. The advantages of the addition of strontium and its substitution in the crystal lattice of colemanite represent a method for controlling and tailoring the properties of this material for obtaining a peak response of a pyroelectric detector at some predetermined temperature between +35 C. and -35 C. Also, the operation of ferroelectric memory elements from the strontium isomorph may be used at or near room temperature.

The strontium isomorph, Compound I (ZSrO- 3B O SH O) of colemanite replacement of calcium by strontium) can be synthesized by several reactions. The following related strontium borate hydrates may also be prepared as given in Table of Reactions:

Compound III (SrO-3B O -4H O), Reaction No. 9.

Compound IV (SrO-3B O -4H O),' tunellite, Reaction Compound V (SrO-B O -4H O), Reaction No. 15.

Compound VI (SrO-B O -4H O), Reaction No. 11.

Any one of these compounds is converted to Compound I (2SrO-3B O -5H O) by the action of borax solution as present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The synthesis of the strontium isomorph of colemanite, which represents 100% replacement of the calcium with strontium by,

(a) reacting a compound from the group consisting of (-b) filtering, washing, and drying the crystalline reaction product 2SrO- 313 0 5H O.

2. The synthesis of the strontium isomorph of colemanite, which represents 100% replacement of the calcium with strontium by,

(a) reacting Sr(IO -H O with approximately 2.6%

borax solution at 65 C. for approximately 14 days,

(b) filtering, washing, and drying the crystalline reaction product ZSrO 3'B O SH O.

3. The synthesis of the strontium isomorph of colemanite, which represents 100% replacement of the calcium with strontium by,

(a) reacting a compound from the group consisting of SrCl and Sr(NO with approximately 5.4% borax solution 80 C. for approximately 36 days,

(b) filtering, washing, and drying the crystalline reaction product 2SrO-6B O -5H O.

References Cited Christ: The American Mineralogist, vol. 45, March- April 1960, pages 334-340.

Hart et al.: Journal of Inorganic & Narc. Chemistry, vol. 24, 1962, pages 10571067.

Parkerson: U.S. Naval Ordnance Laboratory, Tech. Memo, No. 42-24, January 1959, pages 18.

Parkerson: US. Naval Ordnance Laboratory, Tech. Memo, No. 42-31, June 1959, pages 1-8.

..3 .4 and s oqg o 41.1 0 with OSCAR R. VERTIZ, Primary Examiner.

proximately 1.5 to 3% borax solution at C. from approximately 8 to 27 days,

H. T. CARTER, Assistan Examiner. 

1. THE SYNTHESIS OF THE STRONTIUM ISOMOPH OF COLEMANITE, WHICH REPRESENTS 100% REPLACEMENT OF THE CALCIUM WITH STRONTIUM BY, (A) REACTING A COMPOUND FROM THE GROUP CONSISTING OF SRO$3B2O3$4H2O AND SRO$B2O3$4H2O WITH APPROXIMATELY 1.5 TO 3% BORAX SOLUTION AT 65*C. FROM APPROXIMATELY 8 TO 27 DAYS. (B) FILTERING, WASHING, AND DRYING THE CRYSTALLINE REACTION PRODUCT 2SRO$3B2O3$5H2O.
 2. THE SYNTHESIS OF THE STRONTIUM ISOMORPH OF COLEMANITE, WHICH REPRESENTS 100% REPLACEMENT OF THE CALCIUM WITH STRONTIUM BY, (A) REACTING SR(IO3)2$H2O WITH APPROXIMATELY 2.6% BORAX SOLUTION AT 65*C. FOR APPROXIMATELY 14 DAYS, (B) FILTERING, WASHING, AND DRYING THE CRYSTALLINE REACTION PRODUCT 2SRO$3B2O3$5H2O.
 3. THE SYNTHESIS OF THE STRONTIUM ISOMORPH OF COLEMANITE, WHICH REPRESENTS 100% REPLACEMENT OF THE CALCIUM WITH STRONTIUM BY, (A) REACTING A COMPOUND FROM THE GROUP CONSISTING OF SRCL2 AND SR(NO3)2 WITH APPROXIMATELY 5.4% BORAX SOLUTION 80*C. FOR APPROXIMATELY 36 DAYS, (B) FILTERING, WSHNG, AND DRYING THE CRYSTALLINE RECTION PRODUCT 2SRO$3B2O3$5H2O. 